Evaluate library to manage CLI configuration

[dblandin]

We currently have our own config utility (built to store an Artsy API token. As we continue to grow the CLI, we might want to consider a library to mange that config management for us.

We currently refer to process.env for the following tokens: GITHUB_TOKEN, OPSGENIE_API_KEY, CLIENT_ID, CLIENT_SECRET, SLACK_WEB_API_TOKEN. I don't think it's reasonable to expect the user to have all of these environment variables set on their system. It would be great if we could check for their presence when needed, and guide to the user on how to fetch them.

I'm thinking of something like the aws configure flow with interactive prompts.

Check out the Config section in this cheatsheet for options: https://github.com/sw-yx/cli-cheatsheet#contextconfig